1. Field of the Invention
This invention relates to ceramic materials, particularly suitable for use as cutting tools.
2. Description of the Prior Art
Cutting Tools made of alumina, well known as one of the ceramics for cutting tools, are excellent in abrasion resistance, but, on the other hand, have a disadvantage of being susceptible to chipping. For this reason, the impovement in toughness has been one of the main objectives of developmental work on ceramic tools from the early stage of their development until now. As one of solutions to the problem, there was invented a ceramic tool of an alumina-titanium carbide (Al.sub.2 O.sub.3 -TiC) type with an improved resistance to the chipping caused by thermal shock, in which alumina was incorporated with about 30% by weight of titanium carbide to reduce the size of crystal grains as well as to reduce the decline in thermal conductivity with the increase in temperature said decline originating from the inherent properties of alumina.
As compared with a so-called "white-type" ceramic tool made of alumina alone, the ceraminc tool of the Al.sub.2 O.sub.3 -TiC type has a higher toughness and a higher resistance to the chipping failure caused by thermal shock. As a consequence, this type of tool has exhibited its usefulness especially in such uses as turning of high-hardness materials and milling of cast iron materials, both of which are hardly machinable by means of "white" ceramic tools. However, even such a ceramic tool of an Al.sub.2 O.sub.3 -TiC type has a disadvantage of being susceptible to boundary abrasion in the area of machining a high-hardness material under such machining conditions that the temperature of cutting edges exceeds 1,200.degree. C., because the high-temperature hardness of TiC incorporated in a considerable amount becomes lower than that of alumina, resulting in deterioration of the abrasion resistance of the tool.